212 



Canadian forestry Journal, May, jp20. 



Inspecting lumber at Prince Rupert to determine its suitability for aeroplane construction. During 

 the war, the high character of this inspection, on which human lives depended, won universal 

 commendation. 



factor of safety to permit some de- 

 fects in the material. In aeroplane 

 construction, however, the reduction 

 weight and wind resistance to the 

 minimum is of such paramount im- 

 portance that the size of each com- 

 ponent must be so reduced that only- 

 flawless material can be used. The 

 stresses are carefuly computed for 

 every portion of the various parts, 

 and all unnecessary wood is removed 

 as shown in the illustrations. 



In addition to the ordinary defects 

 recognized in lumber, "angling" grain 

 is perhaps the most serious defect in 

 aeroplane wood. By sawing parallel 

 to the bark it is comparatively easy 

 to get the grain formed by the an- 

 nual rings to run straight, but there 

 is a tendency for trees to grow in a 

 more or less spiral form which causes 

 the fibres to angle across the flat 

 grain or tangential faces of sawn 

 lumber. Except; where the spiral is 

 very slight, it is impossible to cor- 

 rect this by any method of sawing. 

 On account of these specially rigid 

 .requirements, the percentage of any 



kind (»f lumber that can be used for 

 this purpose is very small. 



Civil Aviation's Wood Needs. 



Though with the cessation of the 

 war the demand for wood for aero- 

 plane construction has practically 

 ceased, there is no doubt that com- 

 mercial aeronautics will develop into 

 a very important industry demanding 

 large supplies of high grade wood. A 

 great number of kinds of woods are 

 used for different purposes, but for 

 the framework of the wings and fuse- 

 lage, spruce has been found the rnost 

 suitable on account of its combina- 

 tion light weight, tensile strength, 

 flexibility and resistance to shock and 

 splitting!^ Of the American species, 

 white spruce, red spruce and Sitka 

 spruce have been found almost equal- 

 ly satisfactory, but the higher per- 

 centage of clear and the large sizes 

 obtainable in the Sitka spruce make 

 it by far the most important species. 



The difficulty of securing sufficient 

 spruce of the required quality led to 



